1. Field of the Invention
The present invention relates to a dielectric/barrier rib composition for a plasma display panel, and more particularly to a composition used for forming a transparent dielectric layer and a barrier rib on an electrode for a plasma display panel.
2. Description of the Related Art
A transparent dielectric for a plasma display panel is disposed on a front panel having an ITO (Indium Tin Oxide) and metal electrode patterned thereon and is made by calcining glass paste, including glass powder having a maximum particle size smaller than an average thickness of a film thereof, to form a film having a thickness of 20 μm to 40 μm, in order to secure high transparency. The glass paste is a mixture of PbO—B2O3—SiO2 based glass powder containing an excess amount of PbO and a filler, an organic solvent and a polymeric resin. The dielectric film is made by forming a thick film on the glass substrate by a screen printing method using the glass paste followed by calcination at a high temperature of 500° C. to 600° C. To obtain high transparency in the dielectric film, it is important to remove bubbles contained in the dielectric layer. It is also important to precisely control composition, particle size, conditions for manufacturing and calcination of glass powder, etc.
A front panel dielectric of an alternating current type plasma display panel forms a wall charge, thereby maintaining discharge-holding voltage, and serves to protect the electrode from ion bombardment occurring upon discharging. Conventionally, the dielectric layer needs to have a thickness of about 40 μm, transmittance of more than 80%, and DC breakdown voltage greater than 5 kV.
Breakdown voltage of front panel dielectric is a very critical factor in driving the plasma display panel. For the dielectric utilizing glass paste, the breakdown voltage is decreased due to bubbles produced by calcining conditions and surface conditions of the glass powder. Also, metal Pb remaining inside the film after calcination lowers the breakdown voltage of the dielectric layer, thus resulting in deterioration of dielectric performance.
When utilizing a frit containing a low melting point glass as a main component, it is still difficult to obtain a low temperature calcination type transparent dielectric material without addition of an excess amount of Pb. Similarly, the low melting point glass paste also requires high temperature calcination at a temperature of 550° C. to 580° C. A thermal hysteresis process at high temperature of more than 500° C. causes many disadvantages such as changes in the dimensions of the glass substrate, patterns that cross each other which results in defective display panels, and difficulty in realizing a large screen of the panel.
The low melting point glass containing primarily Pb has disadvantages such as a high dielectric constant of 10 to 12 and increased power consumption of the device due to generation of high current upon discharging. In particular, the manufacturing of the barrier rib of the back panel produces a large amount of waste materials, thus increasing environmental contamination and waste material disposal costs. Japanese Patent Publication Laid-Open Nos. Hei 9-199037 and 9-278482 propose Na2O—B2O3—SiO2 based glass and Na2O—B2O3—ZnO based glass, having lower dielectric constants than conventional compositions and softening points of 500° C. to 600° C. Both glass compositions contain no Pb component. These glass compositions contain a softening point lowering component composed of an alkaline metal oxide such as Na2O, K2O and Li2O added thereto, and thus it is possible to perform calcination of the dielectric layer at a relatively low temperature. However, when glass to which a softening point lowering component has been added is used in the dielectric layer, there is a possibility of yellowing in the dielectric layer or front glass panel. Glass compositions containing a softening point lowering component base limit the use of general substrates such as inexpensive soda lime glass or plastic substrate due to the high calcination temperature of more than 500° C.
Further, International Patent Application PCT/JP2002/006666 proposes zinc oxide, boron oxide, lithium oxide, sodium oxide, potassium oxide, rubidium oxide, cesium oxide, copper oxide, silver oxide, manganese oxide(IV), cerium oxide(IV), tin oxide(IV), and antimony oxide(IV) as components constituting the dielectric, in order to reduce yellowing occurring in Na2O—B2O3—SiO2 based glass and Na2O—B2O3—ZnO based glass. These materials also require a high calcination temperature of more than 500° C.
Screen-printing is usually used to form the dielectric layer employing the low melting point glass paste, but this process is very complicated due to formation of a thick film by repeated printing more than two times. In particular, the barrier rib of the back panel requires a relatively thick film as compared to the dielectric layer, and requires printing about eight times. However, the film utilizing glass paste shows changes in the flatness of the surface thereof depending on calcination conditions, thus careful attention is required in performing the process. In order to complement such a disadvantage seen in this screen printing method, Japanese Patent Publication Laid-Open No. 97-102273 discloses a process for preparing a plasma display panel comprising applying a glass paste composition on a support film, drying the coated film to form a material layer for forming a film on the support film, transferring the material layer thus formed onto the surface of the glass substrate having an electrode fixed thereon, and calcining the transferred film-formation material layer to form the dielectric layer on the surface of the glass substrate (Dry Film Process). This transfer method using a dry film simplifies the process, however, defects still occur in the dielectric due to calcination conditions because of the use of the conventional low melting point glass paste.
In addition, high power consumption of the plasma display panel functions as a disadvantage compared to a liquid crystal display (LCD) or organic OLED display device. High power consumption is due to the high dielectric constant of the dielectric layer (more than 10). Lowering the dielectric constant below 5 can reduce power consumption.
International Patent Application PCT/JP2001/02289 and Korean Patent Application 2002-46902 propose a dielectric and barrier rib composition capable of calcining even at a significantly lower temperature than a conventional low melting point glass containing Pb, and having a dielectric constant of less than 5, by using a silicon resin and inorganic/organic hybrid materials. This application also proposes a variety of processes for forming the dielectric, such as spin coating, bar coating and application in addition to a conventional printing method. Additionally, this technique has advantages in that it is highly applicable to the transfer method by the above-mentioned dry film and can reduce the decreased breakdown voltage due to bubbles upon calcining. When the silicon based resin or inorganic/organic hybrid material is used as the dielectric composition, conventional problems such as environmental contamination due to Pb component, deterioration of dielectric functions, high power consumption due to high dielectric constant, variations in precise dimensions due to high calcination temperature and substrate limitation can be resolved. In particular, low temperature calcination allows using plastics or soda lime glass substrate, thus being capable of lowering production costs of the plasma display panel.
Barrier rib material used in the back panel of the plasma display is prepared by adding a white or black pigment to the dielectric composition conventionally used in the front panel. Processes for preparing a variety of barrier rib shapes relative to the composition thereof have been proposed. The barrier rib structure is a structure formed on the dielectric covering a conventional electrode that is formed on a back panel glass having an address electrode patterned in parallel thereon. The barrier rib is disposed to maintain a discharge distance within the panel and prevent electrical and optical interference between adjacent cells. In some embodiments, it has a width of 70 μm to 100 μm and a height of 120 μm to 200 μm. In the case of 42 inch panels, conventionally, the dielectric layer corresponding to the total height of the barrier rib is made using the screen-printing method and then a barrier rib structure is formed using a sandblasting method. However, in preparing a HDTV grade plasma display panel having a size greater than 60 inches, smaller pitches between the structures and very low surface roughness are required, the screen printing through multi-layer printing or the sandblasting method is not suitable for preparing complex structures having precise dimensions.
In order to resolve complexity of the process due to the complicated multi-layer screen printing and the problems associated with uniform formation of the barrier rib dielectric over the entire panel, Japanese Patent Publication Laid-Open Nos. Hei 9-102273 and Hei 9-101653 suggest forming the barrier rib layer in a single process through the above-mentioned transfer film (a composite film composed of a film forming material layer obtained from the glass paste composition and support film, and a cover film laminated on the surface of the film forming material layer so as to be easily peeled off therefrom). Even though this method can simplify the process, it is not possible to avoid disadvantages such as limitation of substrate represented by the calcined low melting point glass, difficulty in patterning a microstructure, surface flatness, and the production of a large amount of environmental contamination waste material. Therefore, development of a material capable of obtaining high thickness in a single process and easy micropatterning is necessary for preparing a large screen high definition plasma display panel.